where can I find the edit menu in blender 2.9
This is the Tool Shelf, and has been replaced in the 2.80+ default interface by a more condensed Tool Shelf that uses gizmos, the various menus at the top of the 3D View, and the operations search engine. Check out The Blender Documentation page for advanced details, or comment below.
If you are opening an old blend file with a newer version of blender, try turning off “load UI“ in the file browser, so you will get the new default interface set up. You would want this, because many editors are quite different in 2.80 then they were in 2.79.